Certain complaints about building water supply systems (BWSSs) arise from their oversizing or undersizing. It is essential to improve their efficiency by way of minimizing their cost and maximizing the benefit accrued from them. This work introduces practical guidelines for BWSSs design, which deal not only with the cost optimization but also with water availability during high demands. A head-dependent analysis function, which takes into consideration the pressure dependency of nodal outflows, is presented. A resilience index, minimum surplus head, and failure index are used to express the capability of BWSSs of overcoming peak demand conditions. The proposed approach was applied on a direct BWSS within three identical residential floors at different levels. It was found that, the internal pipes are preferable to have the same diameter while the main riser of each floor must be increased as the height of the floor increases.